Pot Popular for Pain in Fibromyalgia

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This study found that 13% of patients with a diagnosis of fibromyalgia use cannabinoids, particularly for pain relief, either by smoking the cannabis herb or taking synthetic prescription formulations.

Note that current unstable mental illness, opioid drug-seeking behavior, and male gender were all associated with smoking marijuana.

Use of cannabinoids for medicinal purposes -- particularly for pain relief -- is popular among patients with fibromyalgia, who either smoke marijuana or take synthetic prescription formulations, a Canadian study found.

Among 457 patients referred to a fibromyalgia clinic, 13% self-reported using cannabinoids, according to Mary-Ann Fitzcharles, MB ChB, from McGill University in Montreal, and colleagues.

A total of 80% were marijuana smokers, 24% used prescription formulations, and 3% used both, the researchers reported online in Arthritis Care & Research.

Numerous therapies have been tried and advocated for use in fibromyalgia, but no single approach has proven reliably successful, so many patients turn to nonmainstream remedies.

The rationale for the use of cannabinoids in pain conditions lies in the endogenous cannabinoid system, which consists of a variety of receptors and ligands widely distributed in the central and peripheral nervous system.

"The cannabinoid system has known modulatory effects on pain, inflammation, immune function, and even joint damage. It is therefore reasonable to question whether the effects of cannabinoid agonists, either natural or synthetic, may have relevance to the management of patients with pain conditions such as [fibromyalgia]," Fitzcharles and colleagues stated.

They previously reported on widespread opioid use among patients with fibromyalgia and noted that some also were using marijuana illegally for pain relief. To ascertain the extent of cannabinoid use among this group of patients, they conducted a chart review of patients seen between 2005 and 2010.

Patients initially were evaluated by a rheumatologist to confirm whether or not they met the American College of Rheumatology's criteria for fibromyalgia, and 66% did so.

They also were seen by a psychologist to identify potential underlying mental health difficulties.

Among those not meeting the criteria for fibromyalgia, alternate diagnoses included regional pain syndromes, rheumatic diseases, neurologic abnormalities, and unstable psychiatric disorders.

Patients whose fibromyalgia diagnosis was confirmed had an average functional score of 65.7 out of 100 on the Fibromyalgia Impact Questionnaire and a mean pain score of 6.4 out of 10 on a visual analog scale.

On average, they were receiving 1.9 prescription drugs for symptomatic relief.

Almost one-quarter of patients were diagnosed with a current unstable mental disorder, and 6% overall evidenced opioid-seeking behavior.

Three-quarters of the patients classified with opioid-seeking behavior also had a diagnosis of mental disorder, and two-thirds had a history of substance abuse.

A total of 33% of men with fibromyalgia reported using cannabinoids compared with 11% of women (P=0.0006), with the herbal product being used by 30% and 8% (P=0.0002), respectively.

The amount typically used among marijuana smokers was about a gram per day.

Concomitant opioids were being taken by 47% of all cannabinoid users, including 10 of the 14 on the prescription formulations. Opioids have been prescribed increasingly for patients with fibromyalgia, despite the fact that they are not recommended in current guidelines.

And when used with cannabinoids, uncertain and possibly additive effects on cognition and mood could occur, according to the researchers.

Marijuana smoking was associated with these factors:

Younger age (44 versus 48 years, P=0.02)

Male sex (26% versus 7%, P=0.0002)

Opioid-seeking behavior (17% versus 4%, P=0.001)

Mental illness (36% versus 23%, P=0.002)

Among opioid drug-seeking patients, 13 claimed to have fibromyalgia but had inconsistent evidence of actual pain.

A total of 77% of patients using marijuana were unemployed, suggesting "either the absence of a favorable effect on function or more serious functional impairment among those using cannabis," the researchers observed.

The authors noted that it is "understandable" that patients turn to therapies such as cannabinoids, given the imperfect therapies available for fibromyalgia and the reputation of these substances as pain relievers and aids for insomnia and stress reduction.

Indeed, in small studies the synthetic cannabinoids were shown to reduce pain and improve function, with improvements in sleep similar to those seen with amitriptyline.

However, the use of cannabinoids by individuals with unstable mental illness was "of great concern," according to the researchers.

Also concerning was the finding that one-third of patients referred to a specialty fibromyalgia clinic had been diagnosed erroneously.

"This prevalent inaccuracy in diagnosing [fibromyalgia] attests to the continued challenges associated with this condition and the possibility that some persons may misrepresent subjective symptoms to healthcare professionals in order to access prescription medication," wrote Fitzcharles and colleagues.

Limitations of the study included a relatively small sample size and its setting in a specialty pain clinic. In addition, the study was cross-sectional and relied on self-report of drug use.

"Although cannabinoids as pharmacologic preparations may offer some therapeutic effect for [fibromyalgia] patients, the current evidence should prompt physicians to examine for global psychosocial well being, and not focus only on the single outcome measure of pain," the researchers concluded.

One author reported receiving salary support from the Louise and Alan Edwards Pain Research Foundation.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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